after the block layer regression[0] seemed to be fixed, the machine appeared to be running fine. But after putting some disk I/O to the system (PowerBook G4) it became unresponsive, I/O wait went up high and I could see that the OOM killer was killing processes. Logging in via SSH was sometimes possible, but the each session was killed shortly after, so I could not do much.

The box finally rebooted itself, the logfile recorded something xfs related in the first backtrace, hence I'm cc'ing the xfs list too: